Uplink transmission from a user equipment

Abstract

There is provided techniques for uplink transmission from a user equipment. A method is performed by the user equipment. The user equipment comprises N1 transmit chains. The method comprises reporting, to a network node, a capability of the user equipment of N2 reference signal ports, where N2>N1. The method comprises receiving configuration from the network node for the user equipment to transmit uplink reference signals using N2 reference signal ports. The method comprises transmitting the uplink reference signals using the N2 reference signal ports mapped to the N1 transmit chains.

Description

[0001] UPLINK TRANSMISSION FROM A USER EQUIPMENT

[0002] TECHNICAL FIELD

[0003] Embodiments presented herein relate to a method, a user equipment, a computer program, and a computer program product for uplink transmission from the user equipment.

[0004] BACKGROUND

[0005] Specifications of the New Radio (NR) air interface up to Release 18 (NR Rel-18) support uplink transmission for 1, 2, 4, or 8 transmit (Tx) chains. For example, an uplink reference signal resource can only be configured with 1, 2, 4, or 8 reference signal ports. A transmit precoding matrix indicator (TPMI) field can only indicate a precoder over 1, 2, 4 or 8 reference signal ports, and a Sounding Reference Signal Resource Indicator (SRI) field can only indicate up to 1, 2, 4 or 8 Sounding Reference Signal (SRS) resources. As an example, unless uplink full-power mode 1 is configured in the user equipment (UE), the number of bits in the downlink control information (DCI) used for indicating the number of uplink data transmission layers and the precoder is determined as follows for codebook based uplink data transmission: 4, 5, or 6 bits if the number of antenna ports is 4, if transform precoding is disabled, and if the higher-layer parameter maxRank in PUSCH-Config information element (IE) is set to 2, 3, or 4 (see, Table 7.3.1.1.2-2 of 3GPP TS 38.212 version 17.2.0), 2, 4, or 5 bits if the number of antenna ports is 4, if transform precoding is disabled or enabled, and if the higher-layer parameter maxRank in PUSCH-Config IE is set to 1 (see, Table 7.3.1.1.2-3 of 3GPP TS 38.212 version 17.2.0), 2 or 4 bits if the number of antenna ports is 2, if transform precoding is disabled, and if the higher-layer parameter maxRank in PUSCH-Config IE is set to 2 (see, Table 7.3.1.1.2-4 of 3GPP TS 38.212 version 17.2.0), 1 or 3 bits if the number of antenna ports is 2, if transform precoding is disabled or enabled, and if the higher-layer parameter maxRank in PUSCH-Config IE is set to 1 (see, Table 7.3.1.1.2-5 of 3GPP TS 38.212 version 17.2.0), and o bits if 1 antenna port is used for uplink data transmission. Here, PUSCH is short for physical uplink shared channel, being an example of an uplink data channel.

[0006] However, commercial UEs, such as smartphones, are generally have only 1 or 2 Tx chains. This is due to factors such as power amplifier cost and power consumption, as well as yielding a device with a limited formfactor. On the other hand, UE chipsets, e.g., for customer premises equipment (CPE) devices targeting fixed wireless access (FWA) deployments, have been developed that support the use of 3 Tx chains. However, uplink transmission using 3 Tx chains in the same frequency band is not supported in NR Rel-18.

[0007] For example, a UE with 3 Tx chains might be connected to a network node (e.g., in an existing deployment), where the network node has not yet implemented support for 3 Tx uplink transmission. Since existing specifications (i.e., up to NR Rel-18) support the UE indicating support for 1, 2, or 4 Tx chains (or antenna ports) and up to 1, 2, or 4 uplink data transmission layers, it is unclear how the UE would perform an uplink transmission in this case. For example, it is unclear how the UE would indicate capability to the network and what type of uplink transmission the UE would be configured with by the network. One alternative is for a UE with 3 Tx chains to turn off one TX chain (or antenna port) and indicate fallback support for 2 Tx chains (or antenna ports) and up to 2 uplink data transmission layers. This approach, however, limits the uplink throughput and reduces the uplink coverage.

[0008] Hence, there is still a need for improved uplink transmissions.

[0009] SUMMARY

[0010] An object of embodiments herein is to address the above issues to provide improved uplink transmissions.

[0011] A particular object is to enable the uplink throughput to be improved for thereby improving the uplink transmissions.

[0012] According to a first aspect there is presented a method for uplink transmission from a UE. The method is performed by the UE. The UE comprises N±transmit chains. The method comprises reporting, to a network node, a capability of the UE of N2reference signal ports, where N2> N . The method comprises receiving configuration from the network node for the UE to transmit uplink reference signals using N2reference signal ports. The method comprises transmitting the uplink reference signals using the N2reference signal ports mapped to the N±transmit chains.

[0013] According to a second aspect there is presented a UE for uplink transmission. The UE comprises N±transmit chains. The UE further comprises processing circuitry. The processing circuitry is configured to cause the UE to report, to a network node, a capability of the UE of N2reference signal ports, where N2> N±. The processing circuitry is configured to cause the UE to receive configuration from the network node for the UE to transmit uplink reference signals using N2reference signal ports. The processing circuitry is configured to cause the UE to transmit the uplink reference signals using the N2reference signal ports mapped to the N±transmit chains.

[0014] According to a third aspect there is presented a UE for uplink transmission. The UE comprises N transmit chains. The UE further comprises a report module configured to report, to a network node, a capability of the UE of N2reference signal ports, where N2> N±. The UE further comprises a receive module configured to receive configuration from the network node for the UE to transmit uplink reference signals using N2reference signal ports. The UE further comprises a transmit module configured to transmit the uplink reference signals using the N2reference signal ports mapped to the N transmit chains.

[0015] According to a fourth aspect there is presented a computer program for uplink transmission from a UE comprising N±transmit chains. The computer program comprises computer code which, when run on processing circuitry of a UE, causes the UE to perform actions. One action comprises the UE to report, to a network node, a capability of the UE of N2reference signal ports, where N2> N±. One action comprises the UE to receive configuration from the network node for the UE to transmit uplink reference signals using N2reference signal ports. One action comprises the UE to transmit the uplink reference signals using the N2reference signal ports mapped to the N transmit chains.

[0016] According to a fifth aspect there is presented a computer program product comprising a computer program according to the fourth aspect and a computer readable storage medium on which the computer program is stored. The computer readable storage medium could be a non-transitory computer readable storage medium. Advantageously, these aspects enable the uplink throughput for a UE with N±Tx chains can be improved, even if the network has not implemented support for uplink transmission using N±Tx chains.

[0017] Other objectives, features and advantages of the enclosed embodiments will be apparent from the following detailed disclosure, from the attached dependent claims as well as from the drawings.

[0018] Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a / an / the element, apparatus, component, means, module, step, etc." are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, module, step, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated.

[0019] BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The inventive concept is now described, by way of example, with reference to the accompanying drawings, in which:

[0021] Fig. 1 is a schematic diagram illustrating a communications network according to embodiments;

[0022] Fig. 2 is a flowchart of methods according to embodiments;

[0023] Figs. 3 and 5 schematically illustrate mappings between reference signal ports and antenna ports according to embodiments;

[0024] Figs. 4 and 6 schematically illustrate transmission combs according to embodiments;

[0025] Fig. 7 is a schematic diagram showing structural units of a user equipment according to an embodiment;

[0026] Fig. 8 is a schematic diagram showing functional modules of a user equipment according to an embodiment; and

[0027] Fig. 9 shows one example of a computer program product comprising computer readable storage medium according to an embodiment. DETAILED DESCRIPTION

[0028] The inventive concept will now be described more fully hereinafter with reference to the accompanying drawings, in which certain embodiments of the inventive concept are shown. This inventive concept may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the inventive concept to those skilled in the art. Like numbers refer to like elements throughout the description. Any step or feature illustrated by dashed lines should be regarded as optional.

[0029] Fig. i is a schematic diagram illustrating, at the top, a communications network too where embodiments presented herein can be applied, and at the bottom, a UE 120. The communications network 100 comprises a network node 110, such as a (radio) access network node, radio base station, base transceiver station, node B (NB), evolved node B (eNB), gNB, access point, access node, integrated access and backhaul (IAB) node, transmission and reception point (TRP), etc. The network node 110 is configured to provide coverage, and thus network access, to UE 120 via an uplink / downlink link 130. The UE 120 might be any of a portable wireless device, mobile station, mobile phone, handset, wireless local loop phone, smartphone, laptop computer, tablet computer, wireless sensor device, Internet of Things device, network equipped vehicle, network equipped gaming control, etc. as long as the UE 120 is capable of implementing the herein disclosed embodiments. In the bottom part of Fig. 1 is provided a block diagram of the UE 120.

[0030] The UE 120 is illustrated as having one antenna panel 122 as connectable to a baseband unit 124 via transmit chains 126. In this respect, the antenna panel 122 is illustrated as an antenna array with four columns and one row of single- or dualpolarized antenna elements 128, and where each of the antenna elements 128 is connectable to the baseband unit 124 via a respective transmit chain 126. This is only one example implementation of the UE 120, and the example implementation is provided to illustrate the herein disclosed embodiments. For example, for the herein disclosed embodiments it is sufficient that the UE 200 has at least N±transmit chains. It is thus noted that the herein disclosed embodiments apply also to other implementation of the UE 120, for example a UE with a two-dimensional antenna panel 122, and / or a UE 120 with more than one antenna panel 122, as long as the UE 120 is capable of implementing the herein disclosed embodiments.

[0031] In some aspects, the capability of multiple-input multiple-output (MIMO) communication is defined in part by the maximum number of (uplink) reference signal ports and the maximum number of (uplink) layers that the UE supports. The maximum number of reference signal ports per reference signal resource identifies the maximum number of antenna ports that the UE can us for an uplink data transmission in codebook-based operation and can be thought of as the number of Tx chains in the UE for common UE implementations. As mentioned above, NR Rel-18 supports the capability for the maximum number of reference signal ports in one reference signal resource to be one of {1, 2, or 4} ports, corresponding to the reference signal resource configurations supported in NR Rel-18. Likewise, the maximum number of layers supported by the UE can be one of {1, 2, or 4} layers. Consequently, for a UE to be compliant with UE capability for codebook-based uplink MIMO transmission according to NR Rel-18, the UE cannot declare support for 3 MIMO layers. On the other hand, if the UE has 3 Tx chains, as will be disclosed in more detail hereinafter, the UE could still declare support for e.g., 4 reference signal ports in one reference signal resource. The UE would then map the 4 reference signal ports onto its 3 Tx chains.

[0032] At least some of the herein disclosed embodiments therefore relate to a UE with N±transmit (Tx) chains (and, optionally, capable of transmitting L±= N±uplink (UL) data transmission layers) that to the network reports capability for UL transmission with N2> N Tx chains, that by the network is configured with 7V2-port UL transmission but that performs UL transmission using only N±Tx chains. Hence, at least some of the herein disclosed embodiments are based on a UE with a smaller number of Tx chains reporting a capability for a larger number of Tx chains, thus allowing the network to configure UL transmissions for the larger number of Tx chains but the UE actually using only the smaller number of Tx chains for the following UL transmissions. At least some of the herein disclosed embodiments, aspects, and examples use SRS and uplink data transmissions as examples of uplink transmissions using the fewer than reported number of Tx chains. For illustrative purposes, some of the examples refer to a UE with three Tx chains reporting support for four Tx chains, however, the herein disclosed embodiments are applicable to a UE with q TX chains reporting support for N2> N±Tx chains. Furthermore, in some aspects, as in the context of radio access network working group 4 (RAN WG4) specifications, such as specified in 3GPP TS 38.101-1, version 18.3.0, with connectorized requirements, transmitting on a Tx chain is equivalent to transmitting on an antenna port, and so the examples herein can be interchangeably characterized in such cases as transmitting on either antenna ports or Tx chains.

[0033] The embodiments disclosed herein in particular relate to techniques for uplink transmission from a user equipment 120, 700, 800. In order to obtain such techniques, there is provided a user equipment 120, 700, 800, a method performed by the user equipment 120, 700, 800, a computer program product comprising code, for example in the form of a computer program, that when run on a user equipment 120, 700, 800, causes the user equipment 120, 700, 800 to perform the method.

[0034] Fig. 2 is a flowchart illustrating embodiments of methods for uplink transmission from a user equipment 120, 700, 800. The methods are performed by the user equipment 120, 700, 800. The user equipment 120, 700, 800 comprises N±transmit chains. The methods are advantageously provided as computer programs 920.

[0035] S102: The user equipment 120, 700, 800 reports, to a network node 110, a capability of the user equipment 120, 700, 800 of N2reference signal ports, where N2> N .

[0036] S104: The user equipment 120, 700, 800 receives configuration from the network node 110 for the user equipment 120, 700, 800 to transmit uplink reference signals using N2reference signal ports.

[0037] S114: The user equipment 120, 700, 800 transmits the uplink reference signals using the N2reference signal ports mapped to the N±transmit chains.

[0038] Embodiments relating to further details of uplink transmission from a user equipment 120, 700, 800 as performed by the user equipment 120, 700, 800 will now be disclosed with continued reference to Fig. 2.

[0039] There can be different ways for the UE to report the capability in step S102. In some non-limiting examples, reporting the capability in step S102 comprising at least one of: reporting that the UE is capable of a maximum number of reference signal ports per uplink reference signal resource of N2reference signal ports and is capable of transmitting an uplink reference signal with at most N2reference signal ports, and reporting that the UE is capable of a maximum number of simultaneously transmitted uplink reference signal resources at one symbol of N2uplink reference signal resources and is capable of transmitting at most N2uplink reference signal resources, each comprising one reference signal port.

[0040] If a UE indicates a maximum 2-layer capability and up to 4 SRS ports per SRS resource, the UE would be compliant with 3GPP specifications. Then the network may hypothesize that the UE could support 3 layers instead and could test this by attempting to configure the UE with maxRank or maxMIMO-Layers set to 3. If the UE rejects the configuration, e.g., by sending an RRCReestablishmentRequest with a ReestablishmentCause set to ‘reconfigurationFailure’, then the network could infer that the UE could not transmit 3 layers, while if it accepts the configuration, e.g., by sending an RRCReconfigurationComplete message, the UE should be able to support 3 layers. In this way, a UE can report that it is capable of 2 layers, but still operate with 3 layers. Therefore, in some examples, a UE with 3 Tx chains reports a UE capability that it supports up to 2 layers for uplink data transmission, and also a maximum number of reference signal ports per resource of 4 ports. However, the UE transmits up to 3 layers when indicated to do so by the network. In some such examples, the UE accepts a configuration that sets a maximum number of 3 uplink data transmission layers for the UE.

[0041] For non-codebook-based operation, the maximum number of simultaneously transmitted reference signal resources at one symbol can similarly be thought of as the number of Tx chains in the UE. The maximum number of layers for non- codebook-based operation is defined as a separate UE capability from codebookbased operation, but is also one of {1, 2, or 4} layers as for codebook-based operation. On the other hand, the maximum number of simultaneously transmitted reference signal resources is one of {1, 2, 3, or 4}. Therefore, a 3 Tx UE (i.e., a UE with 3 Tx chains) can declare support for 3 simultaneously transmitted reference signal resources and a maximum of 2 layers according to current UE capability. In this sense, 3 Tx operation is supported in Rel-18 for non-codebook-based operation. This has the shortcoming of not supporting 3 layers, and so does not fully exploit the capability of typical 3 Tx UEs. For codebook-based operation, a primary motivation for UEs to have 3 rather than 2 Tx chains is to support 3 layers. Therefore, if the UE indicates that it is capable of 3 simultaneously transmitted reference signal resources for non-codebook-based operation, the network may check if the UE actually supports 3 layers. The network could do so by attempting to configure the UE with maxRank or maxMIMO-Layers set to 3, since these parameters are also supported for non-codebook-based operation. If the UE rejects the configuration, e.g., by sending an RRCReestablishmentRequest with a ReestablishmentCause set to ‘reconfigurationFailure’, then the network could again infer that the UE could not transmit 3 layers, while if the UE accepts the configuration, e.g., by sending an RRCReconfigurationComplete message, the UE should be able to support 3 layers.

[0042] Therefore, in some examples, a UE with 3 Tx chains reports a UE capability that it supports up 3 simultaneously transmitted reference signal resources for non- codebook-based uplink data transmission, and also that the UE supports a maximal number of supported layers of 2 for the non-codebook transmission scheme. In some such examples, the UE accepts a configuration that sets a maximum number of 3 uplink data transmission layers for the UE.

[0043] The maximum number of layers a UE may transmit whilst still being successfully decoded at the network might be less than the number of Tx chains, but is almost always not greater than the number of Tx chains. This is since if two layers are mapped to the same Tx chain, they would not be separable by a linear receiver in the network node 110. However, as will described in more detail below, if a 3 Tx UE were to transmit e.g., 4 SRS ports and an SRS port is blanked or two SRS ports are mapped to one and the same Tx chain, the network would detect that the effective rank is less than 4 and could avoid indicating to the UE to use 4 layers for an uplink data transmission. In such scenarios, the network may still configure the UE to transmit up to 4 layers for an uplink data transmission and could occasionally schedule the UE to transmit 4 layers. In these cases, the UE should perform the uplink data transmission in a similar way as for an uplink reference signal transmission.

[0044] As will be further disclosed below, in some embodiments, the UE transmits an uplink physical channel, such as a data transmission on a physical uplink shared channel (PUSCH). The actual transmission might be proceeded by the UE receiving configuration from the network node no. In particular, in some aspects, the UE is configured by the network with more layers than the UE can transmit, as in step Sio6 or step Sio8.

[0045] Sio6: The UE receives configuration from the network node no for the UE to transmit the uplink physical channel with at most L2layers, where L < L2.

[0046] In this respect, if the UE blanks a reference signal port by transmitting it with zero power or by not transmitting it, it should also blank the corresponding Tx chain for an uplink data transmission. Therefore, the UE might perform the uplink data transmission by blanking at least one layer. Hence, in some embodiments, transmitting the uplink physical channel (as in step S116) further comprises generating all the L2layers and either: transmitting L2- L±of the L2layers with zero power, or transmitting only L of the L2layers, where L2> L .

[0047] Sio8: The UE receives configuration from the network node no for the UE to transmit the uplink physical channel with at most L2layers, where L = L2.

[0048] In this respect, if the UE maps two reference signal ports to a Tx chain, the UE should combine the two reference signal ports on the Tx chain for performing an uplink data transmission. That is, the UE might perform the uplink data transmission by mapping two layers to one and the same Tx chain. Hence, in some embodiments, transmitting the uplink physical channel (in step S116) further comprises mapping two of the L2layers to one same transmit chains.

[0049] In either case, the UE should generate all layers, including all coded bits for the transport block carried by the layers, as well as the corresponding modulation symbols in the layers. Otherwise, the network would assume an incorrect number of coded bits, which could lead to a decoding failure.

[0050] Therefore, in some examples, a UE with 3 Tx chains reports a UE capability that it supports up to 4 layers for an uplink data transmission, and also a maximum number of reference signal ports per resource of 4 ports. When indicated by the network to perform a 4-layer uplink data transmission, the UE generates all 4 layers and their corresponding modulation symbols but transmits them on its 3 Tx chains. In some aspects, the UE reports capability for fewer layers than it can transmit but transmits using the number of layers it actually can transmit. Hence, in some embodiments, the UE is configured to perform optional step Sno.

[0051] Sno: The UE receives configuration from the network node no for the UE to transmit the uplink physical channel with at most layers, > L2.

[0052] In some aspects, the UE accepts a maxRank or maxMIMO-layers configuration with greater number of layers than it reports capability for. Hence, in some embodiments, the UE is configured to perform optional step S112.

[0053] S112: The UE signals to the network node no that the UE has been configured to transmit the uplink physical channel with at most layers, where L > L2.

[0054] In some examples, the UE reports more reference signal ports than Tx chains and makes an uplink data transmission on the fewer Tx chains than reference signal ports. More specifically, a UE having N transmit chains might perform an uplink data transmission on up to L±spatially multiplexed layers. The UE reports capability for uplink transmission using N2reference signal ports and up to L2layers, where N2> N±. The UE is also configured by the network to transmit uplink reference signals using N2reference signal ports. Lastly, the UE makes an uplink data transmission with up to layers mapped to the N±Tx chains. Hence, in some embodiments, the UE is configured for transmitting up to L spatially multiplexed transmission layers, and the capability of the UE as reported in step S102 indicates that the UE is capable of up to L2spatially multiplexed transmission layers for uplink transmission. Then, in some embodiments, the UE is configured to perform (optional) step S116.

[0055] S116: The UE transmits an uplink physical channel, with at most L layers mapped to the N transmit chains.

[0056] In some examples, transmitting 4 layers on 3 Tx chains comprises transmitting a layer with zero power or transmitting two of the layers on one Tx chain.

[0057] In some examples, the UE indicates reference signal port capability and transmits differently according to codebook or non-codebook-based operation. More specifically, when reporting capability for uplink transmission using N2antenna reference signal ports the UE either: (a) reports that the UE is capable of a maximum number of SRS ports per resource of N2reference signal ports and transmitting an reference signal resource with at most N2ports, or (b) reports that the UE is capable of a maximum number of simultaneous transmitted reference signal resources at one symbol of N2reference signal resources and transmitting at most N2reference signal resources each containing one reference signal port.

[0058] Specific aspects of capability for codebook-based UL precoding will be disclosed next.

[0059] In one example, a UE with 3 Tx chains reports support for up to 4 reference signal ports per reference signal resource (e.g., by using the parameter maxNumberSRS- Ports-PerResource as specified in 3GPP TS 38.306, version 17.6.0, set to 4).

[0060] In one such example, the UE with 3 Tx chains reports support for up to 2 layers for an uplink data transmission with codebook precoding (e.g., by using the parameter maxNumberMIMO-LayersCB-PUSCH as specified in aforementioned 3GPP TS 38.306 set to 2).

[0061] Optionally, in this example, the UE might further respond with an RRCReconfigurationComplete message when configured with the parameter maxRank or maxMIMO-Layers set to 3, where this message and these parameters are as defined in 3GPP TS 38.331, version 17.6.0.

[0062] In an alternative example, a UE with 3 Tx chains reports support for up to 4 layers for an uplink data transmission with codebook precoding (e.g., by using the parameter maxNumberMIMO-LayersCB-PUSCH as specified in aforementioned 3GPP TS 38.306 set to 4). When indicated by the network to make an uplink data transmission on 4 layers, the UE generates all 4 layers and their corresponding modulation symbols but transmits them on its 3 Tx chains by transmitting one layer with zero power or transmitting two of the layers on one and the same Tx chain.

[0063] Specific aspects of capability for non-codebook-based UL precoding will be disclosed next.

[0064] In one example, a UE with 3 Tx chains reports support for up to 4 reference signal resources at one symbol or per reference signal resource set with usage ‘nonCodebook’ (e.g., by setting the parameter maxNumberSimultaneousSRS- ResourceTx or maxNumberSRS-ResourcePerSet as specified in aforementioned 3GPP TS 38.306 to 4).

[0065] In one such example, the UE reports support for up to 2 layers for an uplink data transmission using non-codebook precoding (e.g., by using the parameter maxNumberMIMO-LayersNonCB-PUSCH as specified in aforementioned 3GPP TS 38.306 to 2).

[0066] Optionally, in this example, the UE might further respond with an RRCReconfigurationComplete message when configured with the parameter maxRank or maxMIMO-Layers set to 3, where this message and these parameters are as defined in aforementioned 3GPP TS 38.331.

[0067] In an alternative example, the UE reports support for up to 4 layers for an uplink data transmission using non-codebook precoding (e.g., by using the parameter maxNumberMIMO-LayersNonCB-PUSCH as specified in aforementioned 3GPP TS 38.306 to 2). When indicated by the network to make an uplink data transmission on 4 layers, the UE generates all 4 layers and their corresponding modulation symbols but transmits them on its 3 Tx chains by transmitting one layer with zero power or transmitting two of the layers on one and the same Tx chain.

[0068] Specific aspects of network-transparent 3 Tx SRS transmission for codebook-based precoding will be disclosed next.

[0069] In some examples, a UE with 3 Tx chains configured to transmit 4 reference signal ports (i.e., configured with a 4-port reference signal resource in a reference signal resource set with usage ‘codebook’), does not transmit one of the four reference signal ports, or similarly, transmits the reference signal port with zero power. In Fig. 3 is illustrated an example of a mapping 300 between reference signal ports 310 and antenna ports 320 (corresponding to Tx chains) where the last reference signal port (i.e., SRS port 1003) is not mapped to a Tx chain (and hence not transmitted). In one example, the non-transmitted reference signal port is fixed. For example, the last reference signal port (i.e., SRS port 1003 in the examples of Fig. 3) is not transmitted.

[0070] In Fig. 4 is at reference numeral 400 illustrated an example of a 4-port reference signal resource that has been RRC-configured with transmission comb 4 and cyclic shift o (such that SRS port 1000, 1001, 1002, and 1003 are mapped to cyclic shift o, 3, 6, and 9, respectively) and where SRS port 1003 is not transmitted. This figure also hints at how the reference signals will be received at the network; the measured reference signal power will be high for three of the reference signal ports whereas the reference signal power for the fourth reference signal port will be low. In this way, the network node 110 might only measure noise for the fourth reference signal port. Therefore, in some examples, a UE blanks reference signal ports. More specifically, in some examples the uplink reference signals are sounding reference signals (SRSs), and the UE either transmits N2— N±of the N2SRS ports with zero power or transmits only N of the N2SRS ports. That is, in some embodiments, the uplink reference signals are SRSs, and the reference signal ports are SRS ports, and transmitting the uplink reference signals comprises either: transmitting N2— N of the N2SRS ports with zero power, or transmitting only N±of the N2SRS ports. One benefit with this approach is that reference signal power is maximized for the three transmitted reference signal ports. Indeed, since each Tx chain, i.e., each power amplifier, transmits only one reference signal port, each reference signal port can utilize the full power amplifier power. In some examples, it is the SRS port(s) with highest port number(s) is / are blanked. That is, in some embodiments, the N2— N±SRS ports with highest SRS port index are either not transmitted or transmitted with zero power.

[0071] In one example, the UE splits a linear value of the transmit power equally across the 3 out of 4 reference signal ports. That is, in some examples where the UE blanks N2— N±reference signal ports, the reference signal splits a linear value of the transmit power over the N out of N2SRS ports that are transmitted. Hence, in some embodiments, transmit power of the SRSs is equally divided over the N SRS ports.

[0072] In some examples, to adhere to the above power splitting requirement, the UE maps a plurality of reference signal ports to the same antenna port. An example is provided in Fig. 5. In Fig. 5 is illustrated an example of a mapping 500 between reference signal ports 510 and same antenna ports 520 (corresponding to Tx chains) where the last two reference signal ports (i.e., SRS port 1002 and 1003) are mapped to one and the same Tx chain. In particular, in some embodiments, the uplink reference signals are SRSs, and the reference signal ports are SRS ports, and at least two of the N2SRS ports are mapped to one same transmit chain. In some examples, it is the SRS port(s) with highest port number(s) that is / are mapped to the same Tx chain. Hence, in some embodiments, the at least two of the N2SRS ports that are mapped to one same transmit chain are the at least two SRS ports with highest SRS port index.

[0073] In one example, all reference signal ports are transmitted with the same reference signal power, which implies that the above power splitting rule (i.e., according to Clause 7.3 of 3GPP TS 38.213, version 18.0.0) is satisfied and that the power level for the Tx chain transmitting two reference signal ports is twice that of the power level of the other Tx chains transmitting a single reference signal port. That is, in some embodiments, transmit power of the SRSs is equally divided over the N transmit chains. Assume that the 3 Tx UE is of power class 3 (i.e., supporting maximum 23 dBm output power) and the maximum output power for each of the three power amplifiers are 17, 17 and 20 dBm, respectively. If the UE transmit two reference signal ports on a Tx chain with a maximum of 17 dBm output power, the maximum reference signal output power per reference signal port can be 14 dBm, which limits the maximum used reference signal output power for all four reference signal ports. That is, in some embodiments, transmit power of the SRSs is equally divided over the N2SRS ports. However, this issue could be mitigated in some cases by proper selection of the Tx chain used for transmission of two reference signal ports. In one example, the UE transmits two reference signal ports on a Tx chain that has the largest maximum output power. For example, for a 3 Tx UE with maximum power amplifier output powers of 17, 17 and 20 dBm, respectively, if the UE maps two reference signal ports to the Tx chain with 20 dBm maximum output power, the maximum output power per reference signal port can be 17 dBm (which is the maximum allowed reference signal output power supported for a UE with power class 3 configured with a 4-port reference signal resource). Hence, in some embodiments, the transmit chain that the at least two of the N2SRS ports are mapped to has highest maximum output power of all the transmit chains. In one example, the UE transmits two reference signal ports on a Tx chain that has at least a maximum output power corresponding to half of the maximum allowed output power for the UE power class (which would mean that the UE does not have to reduce the output power per reference signal port compared to a UE with 4 Tx chains).

[0074] In one example, the reference signal ports mapped to one and the same Tx chain are transmitted at lower power (e.g., half of the power) compared to the reference signal ports mapped to different, or separate, Tx chains. This implies that the UE can fully utilize the power amplifier power on all Tx ports, but it may lead the network to believe that the channel gain associated with reference signal ports mapped to one and the same Tx chain is worse compared to the channel gain associated with reference signal ports mapped to separate, or different, Tx chains, which, in turn, may lead the network to configure a lower-rank uplink data transmission (e.g., schedule an uplink data transmission only over reference signal port 1000 and 1001).

[0075] In one example, all reference signal ports are transmitted with the same reference signal power unless the UE is operating at (or close to) full power (e.g., if the UE is at cell edge). In this case, reference signal coverage for the reference signal ports mapped to different, or separate, Tx chains can be improved by being transmitted at a higher power compared to the reference signal ports mapped to one and the same Tx chain.

[0076] In Fig. 6 is at reference numeral 6oo illustrated an example of a 4-port reference signal resource that has been RRC-configured with transmission comb 4 and cyclic shift o (such that SRS port 1000, 1001, 1002, and 1003 are mapped to cyclic shift o, 3, 6, and 9, respectively) and where SRS ports 1002 and 1003 are mapped to one and the same Tx chain and transmitted with less power compared to the SRS ports mapped to different, or separate, Tx chains. In one example, the last two reference signal ports (i.e., SRS port 1002 and 1003 for the example in Fig. 5) are mapped to one and the same Tx chain. In one example, reference signal ports with either even or odd numbers (i.e., SRS port 1000 and 1002, or 1001 and 1003 for the example in Fig. 5) are mapped to one and the same Tx chain. That is, in some embodiments, the at least two of the N2SRS ports that are mapped to one same transmit chain all have either an odd SRS port index or an even SRS port index. One reason for such mappings is that the network may schedule reference signals such that reference signal ports with even and odd numbers are mapped to different comb offsets, respectively, and it may be preferred, depending on UE coherency, to keep reference signal ports transmitted over one and the same Tx chain on the same comb offset (e.g., for transmission comb 8, the same cyclic shift is used by two reference signal ports, but on different comb offsets). Therefore, in some examples, the UE maps multiple reference signal ports to one antenna port (and thus one Tx chain). More specifically, in some examples the uplink reference signals are SRSs, and the UE maps at least two of the N2SRS ports to one Tx chain in the UE.

[0077] It is possible that the 3 Tx UE is partially coherent, such that two of the three Tx chains are mutually coherent, and the third TX chain is non-coherent with respect to the other two TX chains. In this case, in one example, the UE indicates during UE capability signaling that it supports partial coherent codebook subset, e.g., by using the parameter pusch-TransCoherence as specified in aforementioned 3GPP TS 38.306. In one example, when such a UE is configured with a 4-port reference signal resource in a reference signal resource set with usage ‘codebook’, the UE maps two reference signal ports to the two coherent Tx chains such that a coherent precoder can be applied over the two coherent Tx chains (which would correspond to that the UE maps reference signal port 1 and 3, or reference signal ports 2 and 4 of a 4-port reference signal resource to the two coherent Tx chains), and the UE maps the two remaining SRS ports to the non-coherent Tx chain.

[0078] Aspects of network-transparent 3 Tx PUSCH transmission for codebook-based precoding will be disclosed next.

[0079] For dynamically scheduled uplink data transmission, the TPMI in the DCI maps one or more uplink data transmission layers to reference signal ports associated with the most recent reference signal transmission occasion.

[0080] Furthermore, the UE might perform the uplink data transmission on its Tx chains according to how the uplink reference signals are transmitted. Therefore, in some examples where the UE blanks reference signal ports, the UE might perform an uplink data transmission by blanking at least one layer. More specifically, when the UE transmits the uplink data with up to L layers, the UE generates all of the L2layers. The UE then either transmits one of the L2— layers with zero power or transmits only L of the L2layers. In some such examples, the UE is configured for more layers than it can transmit, but transmits using the number of layers it actually can transmit (by blanking one or more layers). More specifically, the UE is configured by the network to transmit the uplink physical channel with up to layers, where L-L < L2. Furthermore, in an alternative example where the UE maps multiple reference signal ports to one and the same Tx chain, the UE maps two layers to one and the same Tx chain. More specifically, when the UE transmits the uplink data with up to Li layers, the UE maps two of the L2layers to one and the same of the N transmit chains. In some such examples, the UE is configured for more layers than it can transmit and maps two layers to one Tx chain. More specifically, the UE is configured by the network to transmit the uplink physical channel with up to layers, where L±= L2.

[0081] The precoder candidates that can be indicated by the TPMI are restricted depending on UE coherency (i.e., non-coherent, partially-coherent, or fully coherent).

[0082] If a 3 Tx UEs transmit 4 reference signal ports according to the above procedures, it follows that the maximum rank of the channel is 3. Ideally, the network should detect that one of the reference signal ports have not been transmitted and therefore not schedule any uplink data transmission over this reference signal port, i.e., not indicate a TPMI that maps an uplink data transmission to more than 3 reference signal ports. The only 4 Tx precoders that satisfy the condition that an uplink data transmission is not mapped to more than 3 reference signal ports for a rank larger than 1 are the set of non-coherent precoders. Therefore, in one example, a 3 Tx UE that reports support for 4 Tx is only reporting non-coherent UE capability (even though the UE might report support for 2 Tx and partially, or fully-coherent, UE capability).

[0083] However, a 3 Tx UE cannot guarantee that the network schedules an uplink data transmission only over reference signal ports that are mapped to different Tx chains. Hence, the UE needs to be able to handle the case when the UE is not scheduled in this way. Below will be disclosed how these situations are handled for non-coherent and partially, or fully-coherent, UEs, respectively.

[0084] For reference, precoding matrices for uplink data transmissions of rank 1—4 are tabulated in Clause 6.3.15 of 3GPP TS 38.211, version 18.0.0.

[0085] If the UE has reported non-coherent UE capability, the network can configure only the following TPMIs. Rank 1: TPMIs 0—3, rank 2: TPMIs 0—5, rank 3: TPMI o, and rank 4: TPMI o. However, only a subset of these TPMIs will map an uplink data transmission to a reference signal port that was not transmitted or to more than one reference signal port that was mapped to one and the same antenna port. For example, if reference signal port 1003 is not transmitted, the problematic TPMIs are as follows. Rank 1: TPMI 3, rank 2: TPMIs 2, 4, and 5, rank 3: (none), and rank 4: TPMI o. The reason for this is that these TPMIs correspond to precoders where only reference signal port 1003 is transmitted. Since for rank 3 there are not problematic TPMIs as the uplink data transmission can be mapped only to the first three reference signal ports, and that is why it can be preferred that a 3 Tx UE does not transmit SRS port 1003.

[0086] If a 3 Tx UE, which is configured with 4 reference signal ports and that transmits only 3 of 4 these reference signal ports, is configured with non-codebook precoding, and where the indicated precoder is such that the uplink data transmission is mapped to an reference signal port which has not been transmitted, the UE does not perform any uplink data transmission over the SRS port that is not transmitted. For noncodebook precoding, this implies that one uplink data transmission layer will not be transmitted, which may often force the network to trigger a data retransmission (with a different TPMI).

[0087] If a 3 Tx UE, which is configured with 4 reference signal ports and that maps two of these 4 reference signal ports to one and the same antenna port, is configured with non-codebook precoding, and where the indicated precoder is such that an uplink data transmission is mapped to both of the reference signal ports mapped to the same antenna port, the UE maps two uplink data transmission layers to this same antenna port. All layers of that uplink data transmission might not be received, which will force the network to trigger a data retransmission (with a different TPMI).

[0088] A 3 Tx UE might split power evenly over all antenna ports for which the UE performs an uplink data transmission with non-zero power (irrespectively of the number of uplink data transmission layers that is mapped to one and the same antenna port).

[0089] If the 3 Tx UE has reported capability for partially-coherent (PC) precoding or fully- coherent (FC) precoding, one uplink data transmission layer can be mapped to more than one antenna port.

[0090] If a 3 Tx UE, which is configured with 4 reference signal ports but that transmits only 3 of 4 these reference signal ports, is configured with PC or FC precoding, and where the indicated precoder is such that one uplink data transmission layer is mapped to a reference signal port which has not been transmitted, if an uplink data transmission layer is mapped to more than one reference signal ports and one of the more than one reference signal ports has not been transmitted, the UE maps the uplink data transmission layer only over the subset of reference signal ports that were transmitted.

[0091] If a 3 Tx UE, which is configured with 4 reference signal ports that maps 2 of 4 these reference signal ports to one and the same antenna port, and is configured with PC or FC precoding, and where the indicated precoder is such that two uplink data transmission layers are mapped to one or both of the reference signal ports mapped to a same antenna port, the UE maps only one of the uplink data transmission layers to the one or both of the reference signal ports mapped to the same antenna port. In one example, the UE maps both of the uplink data transmission layers to the one or both of the reference signal ports mapped to the same antenna port.

[0092] Fig. 7 schematically illustrates, in terms of a number of structural units, the components of a user equipment 700 according to an embodiment. Processing circuitry 710 is provided using any combination of one or more of a suitable central processing unit (CPU), multiprocessor, microcontroller, digital signal processor (DSP), etc., capable of executing software instructions stored in a computer program product 910 (as in Fig. 9), e.g. in the form of a storage medium 730. The processing circuitry 710 may further be provided as at least one application specific integrated circuit (ASIC), or field programmable gate array (FPGA).

[0093] Particularly, the processing circuitry 710 is configured to cause the user equipment 700 to perform a set of operations, or steps, as disclosed above. For example, the storage medium 730 may store the set of operations, and the processing circuitry 710 may be configured to retrieve the set of operations from the storage medium 730 to cause the user equipment 700 to perform the set of operations. The set of operations may be provided as a set of executable instructions.

[0094] Thus the processing circuitry 710 is thereby arranged to execute methods as herein disclosed. The storage medium 730 may also comprise persistent storage, which, for example, can be any single one or combination of magnetic memory, optical memory, solid state memory or even remotely mounted memory. The user equipment 700 may further comprise a communications (comm.) interface 720 at least configured for communications with other entities, functions, nodes, and devices, such as the network node no in Fig. 1. As such the communications interface 720 may comprise one or more transmitters and receivers, comprising analogue and digital components. The processing circuitry 710 controls the general operation of the user equipment 700 e.g. by sending data and control signals to the communications interface 720 and the storage medium 730, by receiving data and reports from the communications interface 720, and by retrieving data and instructions from the storage medium 730. Other components, as well as the related functionality, of the user equipment 700 are omitted in order not to obscure the concepts presented herein.

[0095] Fig. 8 schematically illustrates, in terms of a number of functional modules, the components of a user equipment 800 according to an embodiment. The user equipment 800 of Fig. 8 comprises a number of functional modules; a report module 810 configured to perform step S102, a receive module 820 configured to perform step S104, and a transmit module 870 configured to perform step S114. The user equipment 800 of Fig. 8 may further comprise a number of optional functional modules, such as any of a receive module 830 configured to perform step S106, a receive module 840 configured to perform step S108, a receive module 850 configured to perform step S110, a signal module 860 configured to perform step S112, and a transmit module 880 configured to perform step S116.

[0096] In general terms, each functional module 8io:88omay in one embodiment be implemented only in hardware and in another embodiment with the help of software, i.e., the latter embodiment having computer program instructions stored on the storage medium 730 which when run on the processing circuitry makes the user equipment 700 perform the corresponding steps mentioned above in conjunction with Fig 8. It should also be mentioned that even though the modules correspond to parts of a computer program, they do not need to be separate modules therein, but the way in which they are implemented in software is dependent on the programming language used. Preferably, one or more or all functional modules 8io:88omay be implemented by the processing circuitry 710, possibly in cooperation with the communications interface 720 and / or the storage medium 730. The processing circuitry 710 may thus be configured to from the storage medium 730 fetch instructions as provided by a functional module 810:880 and to execute these instructions, thereby performing any steps as disclosed herein. Fig. 9 shows one example of a computer program product 910 comprising computer readable storage medium 930. On this computer readable storage medium 930, a computer program 920 can be stored, which computer program 920 can cause the processing circuitry 710 and thereto operatively coupled entities and devices, such as the communications interface 720 and the storage medium 730, to execute methods according to embodiments described herein. The computer program 920 and / or computer program product 910 may thus provide means for performing any steps as herein disclosed.

[0097] In the example of Fig. 9, the computer program product 910 is illustrated as an optical disc, such as a CD (compact disc) or a DVD (digital versatile disc) or a Blu-Ray disc. The computer program product 910 could also be embodied as a memory, such as a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM), or an electrically erasable programmable read-only memory (EEPROM) and more particularly as a non-volatile storage medium of a device in an external memory such as a USB (Universal Serial Bus) memory or a Flash memory, such as a compact Flash memory. Thus, while the computer program 920 is here schematically shown as a track on the depicted optical disk, the computer program 920 can be stored in any way which is suitable for the computer program product 910.

[0098] The inventive concept has mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the inventive concept, as defined by the appended patent claims.

Claims

CLAIMS1. A method for uplink transmission from a user equipment (120, 700, 800), the method being performed by the user equipment (120, 700, 800), the user equipment (120, 700, 800) comprising N±transmit chains, the method comprising: reporting (S102), to a network node (110), a capability of the user equipment (120, 700, 800) of N2reference signal ports, where N2> N±; receiving (S104) configuration from the network node (110) for the user equipment (120, 700, 800) to transmit uplink reference signals using N2reference signal ports; and transmitting (S114) the uplink reference signals using the N2reference signal ports mapped to the N±transmit chains.

2. The method according to claim 1, wherein the user equipment (120, 700, 800) is configured for transmitting up to L spatially multiplexed transmission layers, wherein the capability of the user equipment (120, 700, 800) as reported indicates that the user equipment (120, 700, 800) is capable of up to L2spatially multiplexed transmission layers for uplink transmission, and wherein the method further comprises: transmitting (S116) an uplink physical channel, with at most L±layers mapped to the N transmit chains.

3. The method according to claim 1, wherein the uplink reference signals are sounding reference signals, SRSs, and the reference signal ports are SRS ports, and wherein transmitting the uplink reference signals comprises either: transmitting N2— N of the N2SRS ports with zero power, or transmitting only N of the N2SRS ports.

4. The method according to claim 3, wherein the N2— N SRS ports with highest SRS port index are either not transmitted or transmitted with zero power.

5. The method according to claim 3, wherein transmit power of the SRSs is equally divided over the N±SRS ports.

6. The method according to claim 2, wherein the uplink reference signals are sounding reference signals, SRSs, and the reference signal ports are SRS ports, and wherein at least two of the N2SRS ports are mapped to one same transmit chain.

7. The method according to claim 6, wherein said at least two of the N2SRS ports that are mapped to one same transmit chain are the at least two SRS ports with highest SRS port index.

8. The method according to claim 6, wherein said at least two of the N2SRS ports that are mapped to one same transmit chain all have either an odd SRS port index or an even SRS port index.

9. The method according to claim 6, wherein transmit power of the SRSs is equally divided over the N2SRS ports.

10. The method according to claim 6, wherein transmit power of the SRSs is equally divided over the N±transmit chains.

11. The method according to claim 6, wherein said one same transmit chain that said at least two of the N2SRS ports are mapped to has highest maximum output power of all the transmit chains.

12. The method according to claim 2, wherein transmitting the uplink physical channel further comprises generating all the L2layers and either: transmitting L2— L of the L2layers with zero power, or transmitting only L of the L2layers, where L2> L1.

13. The method according to claim 12, wherein the method further comprises: receiving (S106) configuration from the network node (110) for the user equipment (120, 700, 800) to transmit the uplink physical channel with at most L2layers, where L < L2.

14. The method according to claim 2, wherein transmitting the uplink physical channel further comprises mapping two of the L2layers to one same transmit chain.

15. The method according to claim 14, wherein the method further comprises:receiving (Sio8) configuration from the network node (no) for the user equipment (120, 700, 800) to transmit the uplink physical channel with at most L2layers, where L1= L2.

16. The method according to claim 2, wherein the method further comprises: receiving (S110) configuration from the network node (no) for the user equipment (120, 700, 800) to transmit the uplink physical channel with at most L±layers, where L > L2.

17. The method according to claim 16, wherein the method further comprises: signaling (S112) to the network node (no) that the user equipment (120, 700, 800) has been configured to transmit the uplink physical channel with at most L layers, where L > L2.

18. The method according to any preceding claim, wherein reporting the capability comprising at least one of: reporting that the user equipment (120, 700, 800) is capable of a maximum number of reference signal ports per uplink reference signal resource of N2reference signal ports and is capable of transmitting an uplink reference signal with at most N2reference signal ports, and reporting that the user equipment (120, 700, 800) is capable of a maximum number of simultaneously transmitted uplink reference signal resources at one symbol of N2uplink reference signal resources and is capable of transmitting at most N2uplink reference signal resources, each comprising one reference signal port.

19. A user equipment (120, 700) for uplink transmission, the user equipment (120, 700) comprising N transmit chains, the user equipment (120, 700) further comprising processing circuitry (710), the processing circuitry being configured to cause the user equipment (120, 700) to: report, to a network node (110), a capability of the user equipment (120, 700, 800) of N2reference signal ports, where N2> N±; receive configuration from the network node (110) for the user equipment (120, 700, 800) to transmit uplink reference signals using N2reference signal ports; andtransmit the uplink reference signals using the N2reference signal ports mapped to the N transmit chains.

20. A user equipment (120, 800) for uplink transmission, the user equipment (120, 800) comprising N transmit chains, the user equipment (120, 700) further comprising: a report module (810) configured to report, to a network node (110), a capability of the user equipment (120, 700, 800) of N2reference signal ports, where N2> N ; a receive module (820) configured to receive configuration from the network node (110) for the user equipment (120, 700, 800) to transmit uplink reference signals using N2reference signal ports; and a transmit module (870) configured to transmit the uplink reference signals using the N2reference signal ports mapped to the N transmit chains.

21. The user equipment (120, 700, 800) according to claim 19 or 20, further being configured to perform the method according to any of claims 2 to 18.

22. A computer program (920) for uplink transmission from a user equipment (120, 700, 800) comprising N±transmit chains, the computer program comprising computer code which, when run on processing circuitry (710) of the user equipment (120, 700, 800), causes the user equipment (120, 700, 800) to: report (S102), to a network node (110), a capability of the user equipment (120, 700, 800) of N2reference signal ports, where N2> N ; receive (S104) configuration from the network node (110) for the user equipment (120, 700, 800) to transmit uplink reference signals using N2reference signal ports; and transmit (S114) the uplink reference signals using the N2reference signal ports mapped to the N±transmit chains.

23. A computer program product (910) comprising a computer program (920) according to claim 22, and a computer readable storage medium (930) on which the computer program is stored.

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